Dynamically loading dll and calling functions

MonalisaKalla

Hi,

I am dyamically loadning a dll and calling some functions from the dll in QT and VC++ both.
The VC++ code works fine but QT code is not giving me the out put as expected.

Following is the VC++ code:

@
typedef CApiInt* (__cdecl *NewApiConnection1)(); //definig a function pointer

NewApiConnection1 con = (NewApiConnection1) ::GetProcAddress(hInstance, "NewApiConnection") //getting the handle of the function

CApiInt* m_srv = con();//make pointer of the class and it will point to the same where pCtor is pointing

DWORD m_clientNbr;

m_srv->Connect(NULL, &m_clientNbr, NULL);// callig functions of the class.
@

The above code work as expected "NewApiConnection will return CApiInt* , then m_srv will point to the returned CApiInt* and the connect will connect to the

server and increase the client number every time its connect.

Following is the QT code:

@
typedef CApiInt* (__cdecl *NewApiConnection1)();

QLibrary lib( "C:\Program Files\Plus\Oper\bin\Apiud.dll" );
lib.load();

bool bLoaded = lib.isLoaded();

CApiInt* m_srv;
if(bLoaded)
{
    NewApiConnection1 con = (NewApiConnection1) lib.resolve("NewApiConnection");
    if(con)
    {
        m_srv = con();//pointer of the class and it will point to the same where con is pointing
    }


    DWORD m_clientNbr = 0;
    m_srv->Connect(NULL, &m_clientNbr, NULL);
}

@

In the above code m_srv=con() is not behaving the same as in VC++, in VC++ all the data member of objects get intialized and when we call function on top it

behaves correctly, but in QT m_srv is not holding the initialized data members also when i try to see the m_srv contents while debuging it crashes the

application and gives thie message "gdb-i686-pc-minw32.exe has stopped working" closes the program.
And connect does not connect to server clientnumber (m_clientNbr) remains 0.

Please suggest how to resolve this issue w.r.t Qt code.

Thanks in advance.
Monalisa

EDIT: please mark code blocks by @-tags, thanks. Gerolf
EDIT: Move to desktop. Tobias

giesbert

Hi,

first of all, why is this in the forum language binding?

Now to yourt problem:

If I interpret you error description correctly, you are using Qt with mingw. Mingw and MSVC and not 100% compatible. If you only export C-style functions, it could work, but that also depends, how the functions are exported from the library. Can you please show this to us?

Some things I would change in your code:

@
typedef CApiInt* (__cdecl *NewApiConnection1)();

QLibrary lib( "C:\\Program Files\\Plus\\Oper\\bin\\Apiud.dll" );
lib.load();

bool bLoaded = lib.isLoaded();

CApiInt* m_srv = 0; // ensure an initialised pointer
if(bLoaded)
{
    NewApiConnection1 con = (NewApiConnection1) lib.resolve("NewApiConnection");
    if(con)
    {
        m_srv = con();//pointer of the class and it will point to the same where con is pointing
    }

    if(0 != m_srv) // check if it was correctly initialised
    {
        DWORD m_clientNbr = 0;
        m_srv->Connect(NULL, &m_clientNbr, NULL);
    }
}

@

MonalisaKalla

I m sorry for posting on the wrong forum.

I incorporated the code you suggested.

@
if(0 != m_srv) // check if it was correctly initialised
{
DWORD m_clientNbr = 0;
m_srv->Connect(NULL, &m_clientNbr, NULL);
}
@

m_srv is holding a valid address and it is entering into the loop.

When i called the Connect function , it is not connecting and m_clientNbr is remained 0.

Please suggest.

giesbert

then you should debug you library, you are calling

cincirin

Also, be sure your CApiInt exported class follow the rules "here":http://chadaustin.me/cppinterface.html

vikas dhumal

@giesbert How to access external dll in qt (only dll file available dont have header file)
i have vs2013 .net dll named as System.dll without header file. i want to add it in my qt creator application and access all function of dll .please reply

aha_1980

@vikas-dhumal

Please have a look at the QLibrary documentation.

Regards